Talc beneficiation



w. E. BROWN ETAL 3,102,855

TALC BENEFICIATION Filed Sept. 18, 1959 Sept. 3, 1963 United States Patent O 3,162,855 i TAL@ BENEFEQIATEON Whitman E. Brown, Columbus, and Robert D. Macdonald, Worthington, Uhio, assignors, by mesue assrgnments, to Johnson & Johnson, New Brunswick, N .J a corporation of New ersey Filed Sept. 1S, 1959, Ser. No. 840,941 14 Claims. (Cl. 209-164) The present invention relates to talcum powders and, more particularly, to `talcum powders having an improved slip or feel and the method of preparing the same.

`High-grade tales have for many years 4been yused in the form of powder for application to the skin. The talc in its `finely divided form is well suited for this purpose because of its smooth feel. Finely divided talc accordingly has found Kwide application in the cosmetic industry and as ya powder for treat-ing tender skins, such as those of infants, to prevent chafing or yother irritation as would occur from ydiapers or wet clothing. For such uses, particularly where sold as -a baby powder, it is highly desirable to have the talc as free as possible from any irritating particles. The smooth feel of the talcum powder is readily yapparent Iby taking `a pinch of the powder between the thumb and forefinger and sliding the ngers relative to each other. The presence of any small granular or gritty particles can immediately be noticed land gives to the powder a slightly rough or gritty feel. The present invention is directed to producing talcum powders which are substantially free of `any such irritating particles. i.

It has been known that the presence of impurities in talc formations will ygive ltales of poor feel or lubricity. The impurities tend to reduce the slip and give `a somewhat granular or chalky feel to the powder, depending on the degree of fineness to which the powder is ground. The best powders have accordingly been made from the purest natural talc deposits, any improvements in the slip or feel of the talc being obtained through selection of mined talos of higher quality. The highest quality tallcum powders today `are being made from natural talcs, i.e., talos as mined, containing less than 4-5% impurities, the remainder being substantially pure talc.

It has been discovered, however, that not only is the purity of the talc important with respect to obtaining talcum powders `of the most lubricous nature, but the form in which the talc is present is also highly important. Tale in its natural state occurs in three major forms, these being platy talc, fibrous talc, and granular talc. The desirable lubricous nature of the talc results in large part from the talc being present to a large degree `in the platy form. Even though ya talcnm powder may have the desired particle size and be almost 100% pure talc, the presence of even relatively small quantities of granular or fibrous talc will be -found to reduce the lubricity of the talcum powder. As a result, a powder containing granular or fibrous talc will not have as desirable a slip or feel `as does a talcum powder of the same order of talc purity but with a substantially higher platy talc content. The effect of the presence of granular or fibrous talc on the lubricous characteristics of talcum powder can readily be determined by taking` a pinch of `a talcum powder having `about 90% platy talc, the renrainder granular and fibrous talc, and rubbing this between the fingers, then taking Ia sample of talcum powder having a platy ycontent in excess of 96% platy talc, remainder granular and fibrous talc, and repeating the experiment. lt will be noted that the talcum powder with the higher percentage of the Igranular and fibrous talc has a slight gritty feel as compared to the powder with the higher platy content talc. The granular and Patented Sept. 3, 1963 Fice fibrous particles are lapparent :and mar the otherwise smooth feel or slip of the talcurn powder.

Although, the form in which the talc is present, as well as its purity,` affect the lubricity of the final powder, prior to `the present invention there has been no satisfactory way for separating the platy talc from the granular `and fibrous tales with which it lis found in its natural state. Even' the high-grade natural tales presently in general use in this country 'as talcum powders have `at least 10% by weight relatively rough or gritty non-talc impurities and non-platy talc particles. Generally these talcnm powders have a granular or fibrous talc content of about 8-10% by Weight. It is accordingly an object of the present invention to prepare powdered tales of improved lubricity having a platy talc content substantially higher than that found in the heretofore prepared talcum powders. It is a further object to prepare talcumpowders having an improved lappearance and an improved slip or feel. It is also an object of the present invention to provide a process whereby 'granular or brous talcs can be separated from platy talc to substantially increase the platy talc content lof natural talc deposits. It is a further object to provide a process that is relatively inexpensive and ycan be used commercially for upgrading the platy talc content of a powdered talc.

These and other objects and advantages will become more apparent from the following description.

VSince talc has many uses requiring different grades of purity, it has been the practice to separate the talc to varying degree from impurities with which it may be associated in its natural state. The customary milling practice consists of "grinding and sizing, beneflciation generally being obtained by hand sorting and cobbing. Also, because of its ready floatability, froth flotation has been employed to separate the talc from gangue materials, such as tremolite and the alkaline earth carbonates. However, all of these previously employed methods of beneiiciation have been employed to remove `impurities from the talc and not to separate one form of talc from the other. As a result, the final beneficiated talc product still Icontained substantially the same proportion of grannlar and fibrous talc to platy talc that it contained prior to lbeneiiciation, even' though the beneciated talc had most of the gangue removed.

Tale has natural oatability and lends itself readily to flotation processes whereby it is separated from other minerals. However, it has now been discovered `that under certain conditions flotation can be used to separate the platy form of talc from the other `different talc forms. This is indeed surprising when it is `considered that talc floats so readily that -it Ican be floated in waterI alone.

In order to obtain preferential flotation of platy talc Y'from the other forms of talc with which it is naturally associated, it is necessary to use a relatively dilute feed having a sol-id content of less thanyabout 25%. The talc shouldbe 4ground to -a .suicient fneness to liberate the platy from the other forms of talc and, permit flotation. Where the final product is to be used-as a baby powder, it is gener-ally preferred to grind the talc to a particle size lof labout y Tyler mesh or smaller, although flotation can be obtained with particles ground to only about 20 mesh. A substantial .portion of the particles of size smaller than about 10-15 microns should preferably 'be removed prior to flotation. A smfall `amount of a water-soluble frother may be added. The lamount of ifrother should not exceed about 0.10 lb. per ton of solids; otherwise, significant separation' of platy from nonplaty talc will not be obtained. In one manner of practicing the present invention, the initial froth is formed without the yaddition of any frother, and a frother added only enoaaee after the initial froth formedrhas been' removed and the Iamount of froth bein-g formed during the dotation treatment substantially reduced. The frother is then added to again ibuild up the froth to increase the over-all yield of high platy content. Among frothers used in practicing the present invention lare those which are substantially or completely water soluble .and include polypropylene glycol methyl ether, ethyl alcohol, methyl alcohol, n-butyl alcohol and the like.

Although separation of the platy from the non-platy talc can be obtained without the use of depressants, it has been found that the addition of a small amount of certain materials, Such as dextrin, starch, glue, lgua-r gum and the'lilie, to the feed will act to selectively depress the non-platy talc so that a somewhat higher degree yof separation can be obtained. Where depressantsv such :as dextrin are added, they should generally not be used in amounts in excess of the equivalent of 1 lib. of dextrin per rton of solids. Selective depression of the'granular and fibrous talc can lalso `be obtained by control of the pH. It has beenfound that, if the pH is maintained near neutral or at about 6.8 to 8.0 during the flotation, this acts to depress the flotation of the granular and fibrous talc in much the same way as where a depressant, such as dextrin p is added. Care must be taken that the pH not drop to much below .about 6.0. Poor separations of the platy form of talc are obtained with domestic talcs with :a pH of about 6.0 or lower, and when treating tales fhaving a platy content of about 90% by Weight or higher `at such a low pH little or no benefici-ation of the platy contents is obtained. In the preferred practice, the pH is controlled through th'e -addition of hydrochloricV acid in the iarnount necessary to keep the slurry at the desired pH, la. near neutraljslurry generally being preferred. In place of hydrochloric acid, such acids :as hydroliuoric acid, hydrobrornic acid, nitric acid, and the like may Ibo used. The use of depressants alone may not give the ydesired degree of separation of the platy talc. Their use, however, frequently does improve the separation obtained.

Although the removal of fines from the slurry of talc feed is highly beneficial in the selective flotation of platy talc, particularly where the initial platy talc content is relatively high `or Where the solids content of the feed is in excess of about 8% solids, it has been discovered that -substantial'increase in platy content can be obtained by removal of fines alone from ground talcs having la significant amountof fibrous talc. This is apparently due to the fact that in the grinding there is a substantially greater tendency for the fibrous talc Ato be reduced to particle sizes of less than 10 microns than for the platy talc. However, whatever the cause, it is found that if the content of fines of less than 10 micron size is reduced by hydrocen-v trifugal separation from the talc slurry to less` than 10% of the remaining solids the platy talc content of the remaining'talc is substantially enhanced, tales having an initial platy talc content of 90% `and fibrous talc content of 6% being beneflciated to the extent that the talc `so treated has a platy talc content as high as 95%.

Referring to the'flow diagram of the accompanying drawing, the talc is first ground to a particle `size of approximate-ly 200 mesh. This may fbe done in `any conventional mill 10. However, it has been found that the manner of grindingis somewhat critical with respect to the final appearance of theproduct. By Wet grinding the tal?, for example in a pebble mill in the presence of water, ia final product having an appreciably higher luster or gloss can be obtained than obtainable froma powder that has been dry ground in a roller-type mill. The ground product from the pebble mill is passed to a cyclone separator 11 after further dilution with water.` In the separator, particle size of +200 mesh are separated out and returned to the pebble mill for further grinding. The ground talc of -200 mesh particle size is then further diluted with water to a solids content of yabout 10% by weight and passed to a second cyclone separator 12. wherein the very microns, are substantially removed so that the solids content contains less than 10% fines having a size of less than 10 microns. The slurry of talc of 200 mesh with fines removed is then passed to a conditioning tank 13 where it is further diluted.

Where fines have been removed, the feed slurry to the dotation cell can 4contain up to as high as 25% solids although substantially more dilute slurries are preferred. Where fines have not been removed, the particular solids content in the feed slurry to the flo-tation cell is dependent on the initial platy content of the talc being beneiiciated. The solids coutent should not exceed about 8%, if there is to be obtained a preferential separation of platy talc from a high-quality platy talc having an initial platy content of more than about A somewhat higher solids content ymay `be used with lower-quality platy talcs having initial platy contents of less than Iabout 80%. For example, a talc of initial platy content of 46% is beneficiated Without a frother, without the removal of fines, Iand with 13% solids in the feed slurry to provide a talc product of 75-80% platy content, a substantial increase in platy content. However, even with these lower-quality platy talcs of low initial platy content where there is no removal of fines, it generally is preferred that the solids content does not exceed about 15%. An additional fiotation beneiiciation of this 75-80% platy talc product then is carried out at a solids content off less than about 8% to provide a talc product of even higher platy content. The only limit to dilution of the slurry is the practical limit of excess fiuid handling. Generally, a slurry is not used having la solids content of less than 1% a1- though separation could still be obtained.

If .a depressant such las dextrin is to be added, this is preferably added to the slurried talc while it is in the conditioner. Also, any acid depressant, such as hydrochloric acid, added for controlling the pH is preferably added at this stage, although it may if desired be added at any time prior to the actual flotation. As previously stated, it is not necessary to add any acid or other depressant to obtain separation of the non-platy from the platy talc, provided the less than lil-micron particles haveV been removed to less than 10% of the solids and that a suitable amount of frother is used. However, a somewhatV better separation can be :obtained through their use. If these depressantsincluding the hydrocholric acid, Iare used, they should be used with care, since, if present in too large amount-s, they will also act to depress the flotation of the platy talc.

The water suspension of talc preferably remains in the conditioner for a period of time insufficient 4toiresult in la significant pl-i change, i.e., a change in pH from near neutral, and With many ores this is for a period of yabout 1 to 3 minutes. This suspension is then fed into the flotation cell 14. The flotation cell may be of any conventional type wherein the suspension of solids in liquid is agitated 'with lair to produce a froth or foam which floats to the surface. The flotation cell may be a single cell or `a battery .of cells, depending on the size of the operation or the type of cells used. This froth, which is rich in platy talc, is removed las it is formed and passed to a thickener 15, Iwhich is a tank in `which. the froth is permitted to settle, and` the excess water removed. The thickened slurry is then passed to conventional filters 16 where the talc is filtered out.

Excellent separation of the non-platy talc from platy talc in extremely dilute feeds is obtained Without the addition of any frother. However, in order to increase the yield of platy talc, small amounts of a water soluble frother are preferably added. One manner of doing this is to add the frother during the actual flotation after the initially formed froth has `been removed with its initial float of platy talc. In the preferred practice, however-'a small amount of the frothing Iagent is added to the talc in the flotation cell or immediately prior thereto together with a small amount of hydrochloric acid. The frother,

when added, is generally added in amounts of about 0.03 to 0.08 lb. per ton of solids. Further frother may lbe added `during fiotatiou to increase the over-all yield of floated talc. Care should be taken to keep the frothing agent ydown to a minimum needed to maintain the quality; otherwise the Hoa-ted talc will be found to have an undesirable amount of a non-platy talc present. In general, it has been found that if the frothing agent is present in amounts in excess of 0.4 lb. per ton of solids an undesirably high amount of non-platy talc is floated together with the platy talc, poor separation being obtained.

Although separation of platy talc is obtained using conventional city water such, for example, as that found at Columbus, Ohio, which has a total hardness of 95 ppm. and a total solids of 261 ppm., the best results are obtained when demineralized water, demineralized to a resistance of 120,000 to 150,000 ohms per cubic centimeter, is used throughout the dotation step.

The tailings from the flotation cell may be recirculated for further removal of platy talc or this by-product sold for uses other than as body powders such, for example, as in the preparation of lacquers, paints, papers, insecticides, textiles, ceramic compositions, rubber, plastics, etc. These tailings, particularly where the starting material is a good `grade talc, are excellent grade talcs for many uses and are a valuable by-product although they do not contain the high platy content and excellent lubricity which is so desirable for powders which are designed for body application. i

It has been found that the appearance of the final talc product can be improved and a more yglossy appearance imparted if the lter cake is washed with about 3 water displacements `while still on the filter press. Fresh demineralized water is used and the cake washed by passing the fresh demineralized water through the filter cake. Also, any dolomite, which after froth separation is present only in very small amounts, can be substantially completely removed by treating the slurry from the thickener in a leach tank 15a with suicient hydrochloric acid to completely react with the dolomite. This is done `just prior to passage of the slurry to the filters 16 and to washing of the filter cake wit-h water for removal of soluble acid salts. Since generally the dolomite content at this stage is not much in excess of about 0.5% by weight, only a small amount of hydrochloric acid is needed. Care should be taken that only sufficient acid is used to neutralize the dolomite so that the talc itself is not made acidic, In this Way, a powder can be obtained which is substantially neutral. Since the dolomite, if present in amounts in excess of about 0.06% by weight, will impart to moist powder an alkalinity of about 8 to 8.5 pH, it is generally necessary to add a neutralizing agent to the powder to reduce this alkalinity; otherwise, it may cause skin irritation, particularly to tender skins. However, where the dolomite content is reduced to below about 0.06% by weight, the moist powder will remain close to neutral without the addition of a neutralizer.

After filtering, the filter cake can be removed and dried by any conventional drying process and the dried cake broken into powder form. In the preferred practice, drying is done in a spray dryer 18 by first forming a slurry of the filtered talc, in a repulping tank 17, and spraying the slurry into a heated chamber. If a high gloss product is desired, the time during which the talc is kept in the water in forming the slurry and spraying is kept to a minimum, the filter cake being slurried in fresh demineralized water and then immediately sprayed into the drying chamber. The talc -should preferably not be permitted to remain in the slurry tank for more than about l0 minutes. The drying chamber, into which the slurry of talc is sprayed, is generally at a temperature of about 300v to 900 F., the temperature being sufficiently high that the powder is dried while still suspended in the The temperature of the air or lgas introduced into the drying chamber may be as high asV about 1000 F. with the resultant drying chamber temperatures being somewhat less than 1000 F., possibly due to evaporative `cooling within the chamber. However, the temperatures of the introduced air and of the drying chamber should not exceed about 1100c F., otherwise the dried product will be found to have taken on a somewhat gritty feel, to have lost some of its pearly luster, and to be of lower quality. As a result, the dried product will not be as attractive in appearance or as lubricous as a similar product spray dried at a lower temperature. At a temperature of about 1550 F. platy talc is destroyed with transformation to the mineral clinoenstatite, which exhihi-ts gritty properties similar to tremolite.

The substantial improvement in platy talc content obtained by iiotation beneliciation, in accordance with the present invention, is well illustrated by the following table in which the vplaty talc content of different talc ores prior to beneiiciation is compared with the platy talc content after beneciation. It will be noted that in each instance a substantial increase in platy talc is obtained.

TABLE I Platy content (percent by Weig Ore Before flotation After flotation beneciation beneeiatiou The best talcum powders presently available are those prepared from natural tales having a platy content of about 90% It will be noted from the above table that the platy content of these talcs can be substantially increased and talcum powders having a platy content in excess of 98% by weight obtained -by the present process. It will also be noted that talos having platy talc contents of as low as 30% by Weight can be upgraded to where they approach the highest `grade natural talcs in platy talc content by a single flotation step. A second flotation treatment would increase the platy content of these talcs to Well above the 90% platy talc content presently found in the best `grade talcum powders.

The invention is further illustrated by the following examples, other than Example l, which are given by way of illustration only, the invention not being limited thereto.

EXAMPLE I A water slurry is prepared of 200` mesh talc in which the fines have not been removed, the talc having an initial platy content of 90%, a non-platy fibrous talc content of 6%, and 4% by weight of other impurities, consisting mainly of dolomite and tremolite. This slurry is diluted to a solids content of 13% by weight and then passed to a sub-aeration type flotation cell and the froth formed is separated, allowed to settle and filtered. Although the percent of non-talc materials in the fioated talc is appreciably reduced, the platy talc content of the floated talc after substantially `all of the froth is removed is 89% by weight. It is thus apparent that even though this flotation removes impurities other than talc, it is ineffective for separating non-platy from the platy talc.

EXAMPLE II formed is collected over rninute intervals.

. platy talc content of the floated talc is 98%.

7 tent that can be obtained by removal of fines alone where the feed talc contains a significant amount of fibrous talc.

EXAMPLE III Using the same feed talc as in Example I, a slurry of -200 mesh talc is prepared with no removal of fines and the slurry diluted to a solids content of 4.8% by weight. The slurry indeionized water has a natural pH of 8.0 to 8.4. This diluted slurry, without the addition of any reagents is'passed to a subaeration type flotation cell of the same type as that of Example I .and the froth for-med is separated, allowed to settle and filtered. The froth as six minutes, little if any further froth continues to form. The talc removed with the froth has a platy content as follows: j

. Percent platy Froth in first minute 94 Froth in second minute 94 Froth--in third minute 93 Prot-h in fourth minute 93 Froth in fifth minute 93 EXAMPLE IV Froth in first minute 96 Froth in `second minute 9 7 Froth in third minute 97 Froth in fourth minute 97 Froth -in fifth minute 97 EXAMPLE V Using a talcl feed similar to that of Example I with the exception that fines of less than 10 micron size have been reduced 4to less than 10% of the solid-s by centrifugal separation of nes from the slurry the feed is diluted to a solids content of 8%. This diluted slurry is then adjusted to ya pH of 7.6 through the addition of small amounts of hydrochloric acid. To the slurry is also added 0.07 lb. per ton solids of a frother such as polypropylene glycol methyl ethers of average molecular weight of 200. Dowfroth 200 is a generally commercially available material of this type. The slurry is then passed Ito a sub-aeration type flotation `cell and lthe froth formed is separated, allowed to settle and filtered. The When the identical run is repeated except lfor an increase of the frother to `about 0.4 lb. per ton solids, essentially no separation of platy from non-pl-aty talc is obtained.

A talc platelet can =be readily distinguished from a nonplaty talc particle by its characteristic shape or form. While non-talc particles in a talc powder can be determined accurately by chemical analysis, these particles also can be readily identified, distinguished, and approximated by a physical method, such as amicroscope count.

Y .The microscope count has been found to be the best means to date for determining the proportions of platy talc, non-platy talc, land non-talc particles in a talc powder sample of high purity and is the method used in the present specification, all platy talc values in the specication and claims being based on the microscope count method of determination. Inthis procedure, a dry sample of the fine talc powder is dusted onto a glass slide which has been spotted with oil having a refractive index of 1.520. This talc dust is dispersed in .the oil by stirring with a fine probe. The talc sample should be dry to obtain a uniform dispersion in the oil and the sample also should be well mixed so that Ia segregation of sizes is avoided. The oiled sample then is covered with a glass cover plate CII After about the objectives selected for about a magnification of 75 X. Lig-ht is adjusted to refiect through the sample to the eyepiece. The eyepiece having two cross hairs fixed at to each other is focused on the field. Particles which coincide with the cross hairs `are counted and classified as platy talc, fibrous talc, dolomite or tremolite, and sometimes accessory minerals. The cross hairs then are repositioned to a different Ilocation on the same sample and additional particles are counted and classified. Suicient particles are counted and classified to obtain a minimum total count per sample in excess of 300 particles. Counting substantially less than this amount frequently will give erratic results. In low quality talc powder samples having a low, true-platy content, substantially higher counts shouldbe made. Y

To properly identify and classify the various talc and non-talc particles requires care. Nearly whole and large talc platelets are relatively easily distinguished from fibrous or granular talc particles.

Talcum powders prepared in accordance with the present invention are found to have a substantial gloss or luster which is apparent on comparing these products with the talcum powders presently generally available on the market. This gloss or luster is believed to be due to the high percentage of platelike particles present in the product of applicants invention and the low percentage of shards (splintered plates), granular and fibrous talc and other impurities. As a result, the degree of gloss or luster can be considered as a visual indication of the quality of the powder obtained.

This gloss or luster is not only readily apparent but can also be measured with a fair degree of accuracy. Subjective gloss as measured by the human eye is primarily a matter of comparison made by the eye between specular refiection and diffuse refiection from an illuminiated object. This effect of gloss on the `eye and its measurement is discussed in a text entitled Definition and Measurement of Gloss, by V.G.W. Harrison, published by The Printing Allied Trades Research Association, De-

cember 1945, and printed at W. Hefter & Sons Ltd., vCambridge, England. This measurement of gloss is called contrast gloss, contrast gloss index being the ratio of specular reflection to diffuse reflection specular reflection (m-contrast gloss index) Contrast gloss also is defined and discussed in Vthe Journal of Research of the National Bureau of Standards, volume 25, November 1940, Research Paper RP1345, A Multipurpose Photoelectric Reectometer, by Richard S. Hunter, on page 614. Apparatus for measuring this ratio is available commercially and used, for example, by the paper industry for the measurement of paper gloss.

l In obtaining the contrast gloss indexes herein given, a

Gardner Multipurpose Reflectometer (a commercially available instrument, sold by Gardner Laboratory Inc., Bethesda, Maryland, and described in their Bulletin No. 158, for measuring contrast gloss) was used. A standard ceramic plate, having a contrast gloss index of 1.23 upon measurement by a recording goniophotometer, was used as a standard sample to adjust the Gardner Multipurpose Reflectometer to a contrast gloss index reading of 1.23. Contrast gloss index of talcs were measured with this Gardner Multipurpose Rellectometer after this calibration adjustment to the true contrast gloss index (1.23) of the working standard ceramic plate.

A conventional high quality talcum powder, prepared by dry grinding a top-grade talc of platy content of 90% to a particle -size of 200 mesh, is shown to have a contrast gloss index of 1.32, whereas powdered talcs made in accordance with the present invention have contrast gloss indexes of at least 1.40 and some have contrast gloss indexes as big-h as 1.74. The effect of plate content and illustrated bythe following table:

TABLE II Ore Flaty Test content Contrast No. (percent gloss Idcntrli- Treatment by index 1 cation weight) 1 A Dry grinding to 200 microns- 89-90 1. 32 2 A Dry grinding to 200 microns 94 1. 41 and removal of most of micron fines. 3 A Dry grinding to 200 microns, 98-99 1. 47

removal of most of micron fines, and flotation benetlciation. 4 A Wet grinding in pebble mill to 98-99 1. 59 -200 microns, removal of 10 micron rines, and flotation beneticaition. 5.-. B Wet grinding in pebble mill to 99 1. 71 -200 microns, removal of most of -10 micron fines, and flotation benefication.

1 Average of 3 or more measurements.

Although an important aspect of the present invention is the treatment of talcs having an original platy content of about 90% by weight described herein, the invention is not limited to these. The process for separating platy from other forms of talc now makes it possible to use many talc `deposits of inferior grade for body powders that were heretofore considered unsuitable because or" the poor slip or feel of the resulting powder. The platy content of the tales from these deposits can now be substantially increased. The process of the present invention is therefore applicable Wherever it is ydesired to increase the platy talc content of any talc, whether the final use is for body application or otherwise. If platy talc contents in excess of 90% are desired from the poorer grade talc, it may be necessary to carry out the beneficiation ina series of floats rather than a single iioat, which is all that is necessary for talc deposits o-f initial high platy talc content.

Having thus described our invention, we claim:

l. In the treatment of talc to increase the platy talc content, the steps comprising grinding a talc ore to liberate :the platy talc from the other forms of talc and other materials present, removing from said ground ore most of the lfines of particle size of less than 10 microns, forming a dilute slurry of the remaining talc, said slurry having a solids content not exceeding about 25% by weight of said slurry, subjecting said slurry to froth flotation While maintaining the -pH of the slurry within the range of 6.8 to 8.0 during froth flotation, removing froth formed during said froth flotation and separating the talc contained in said floated froth.

2. The process of claim l lin which the pH of the slurry is maintained Within the range of 6.8 to 8.0 through t-he addition of hydrochloric acid.

3. In the treatment of talc to increase the platy talc content, the steps comprising grinding a talc ore to liberate the platy talc from the other forms of talc and other materials present, removing from said `ground ore most of the fines of particle size of less than 10 microns, forming a dilute slurry of the remaining talc, `said slurry having a solids content not exceeding about 25% by weight of said slurry and said slurry containing a Water soluble frother in amounts not appreciably over 0.1 lb. frother Iper ton solids, removing froth formed during said froth flotation and separating the talc contained in said oated froth.

4. The process of claim 3 in which said slurry is maintained at a pH of 6.8 to 8.0 during said froth otation.

5. In the treatment of talc to increase the platy talc content, the steps comprising Wet grinding a talc ore to liberate the platy talc from the other forms of talc yand other materials present, slurrying said ground ore and hydrocentrifugally separating most of the fines of less than l0 micron size therefrom, diluting Ithe slurried ore with nes removed to a solids content of less than 25% by weight solids, adjusting the pH of said diluted slurry to 6.8 to 8.0, subjecting said diluted slurry with adjusted pH to froth flotation, removing froth formed during said froth dotation in the presence of not more than about 0.1 lb. lwater soluble frother per ton of solids, separating the solids from said froth, reslurrying said separated solids and drying said solids by spraying said reslurried solids into a heated chamber.

6. The process of claim 5 in which the drying is done by spraying into a heated chamber having -a temperature within the range of 300 to 1100 F.

7. 'Ihe process of claim 9 :in which the slurry of talc at the time of froth notation has a solids content of not ymore than about 8% by weight.

8. The process of claim 12 in which the pH is controlled by the addition of hydrochloric lacid.

9. In the treatment to increase the platy content of a talc having an initial pl-aty lcontent of less .than about the steps comprising grinding the talc to liberate the platy talc from the other forms of talc and other materials present, forming a slurry of the -ground talc having a solids content not exceeding about 15% by weight, subjecting said slurry to froth flotation, in the absence of `a non Water soluble frother and in the absence of any lfrother in amounts in excess of 0.1 lb. per ton of solids, removing froth formed during said froth flotation and separating the talc contained in said floated froth.

10. In the treatment of talc to increase the platy talc content, the steps comprising grinding a talc Ito liberate the platy talc from the other forms of talc and other materials present, for-ming a slurry of the ground talc having a solids content not exceeding about 8% by weight, subjecting said slurry to froth flotation, in the absence of a non water soluble frother land in the absence of any rother in amounts in excess of 0.1 1b. per ton of solids, removing froth formed during said froth flotation and separating the talc contained in said floated froth.

ll. The process of claim 10 in which the pH of the slurry is maintained within the range of 6.8 to 8.0 during froth notation.

12. A powdered talc containing `less than 10% by weight of lines of particle size of less than 15 microns or less and having a platy talc content in excess of 93% by weight.

13. A powdered talc having a platy talc content of at least 93% and a contrast gloss index of at least 1.40.

14. A powdered talc containing less than 0.06% dolomite and having a platy talc content of 4at least 93% and `a contrast gloss index of at least 1.40.

References Cited in the le of this patent UNITED STATES PATENTS 1,250,216 Peacock Dec. 18, 1917 OTHER REFERENCES Taggart: Handbook of Mineral Dressing, 1947, Section 3, pages -122.

Bulletin of the American Ceramic Society, volume 18, Number 8, August 1939, pages 292-297.

United States Bureau of Mines, Rl. 3314, October 1936.

Bulletin of the American Ceramic Society, volume 22, Number 7, July 15, 1943, pages 223-225, by Gottlieb.

The Story of Sierra Tales, Sierra Tlalc Company, 426 Union League Building, Los Angeles, Calif. 

12. A POWDERED TALC CONTAINING LESS THAN 10% BY WEIGHT OF FINES OF PARTICLES SIZE OF LESS THAN 15 MICRONS OR LESS AND HAVING A PLATY TALC CONTENT IN EXCESS OF 93% BY WEIGHT. 